Erlang 21, Stability and the murder of an innocent Statemachine

Re: Erlang 21, Stability and the murder of an innocent Statemachine

What about documentation from the OTP team that outlines a deprecation policy? It may be a good opportunity to also outline other compatibility guarantees, such as the compiled bytecode guarantees and the node compatibility guarantees, if such are not yet documented.

We did define such document not long ago for Elixir. In terms of deprecations, we have two terms: "soft-deprecation" and "hard-deprecation". The soft-deprecation is added as soon as a new implementation exists. At this point we don't emit any warnings, but we do update the docs to say the feature will warn in the future and start to point folks towards better ways.

A hard-deprecation is when we finally start emitting warnings. A hard-deprecation can only be added after an alternative exists for at least 2 Elixir releases. This is very important because it means that, once a feature is hard deprecated, you know you can use the proposed alternative and that alternative is supported at least two versions back.

This is only necessary if a feature is being replaced. In case a feature is being removed, such as non-smp VM versions, you may skip directly to the "hard-deprecation" and emit warnings straight-away since there won’t be an alternative in the future anyway.

I am not proposing for Erlang/OTP team to follow those rules and conventions but writing *some* rules as minimum guarantees may improve communication and help the community plan in terms of warnings, deprecations and removals accordingly. I would just avoid emitting deprecation warnings in the same version that an alternative is introduced, because it means library developers need to either only support the latest version or introduce conditionals (either at compile-time or runtime) to support multiple versions.

Th point is to phase out gen_fsm. The deprecated
warning is important to get new users to choose
gen_statem. Also if you have a living product you will
probably be better of in the long run changing to
gen_statem. This

is not a complicated change and an exampel of how to do
it is given in the gen_fsm manual page. Of course we give
lots of time to adopt. We have no plan of removing the
gen_fsm code swiftly, it is there in 20 and 21.

I can see the deprecating process needs to enhanchend,
and yes it sort of has more that one purpose which seems
to conflict a bit.

One thing that might help is if we have the ability to deprecate
types which I entered an entry for at
https://bugs.erlang.org/browse/ERL-335 . For example, when all the
time units switched from a format like
milli_seconds to millisecond
in Erlang/OTP 20.0 it would have been easier to have a
deprecated type that can be used for an easier to understand
warning. That may seem like a small issue that can be avoided
by switching to other functions or modules, but often changes
don't need to be large for small changes that can be limited to
type changes.

What about documentation from the OTP team that outlines a deprecation policy? It may be a good opportunity to also outline other compatibility guarantees, such as the compiled bytecode guarantees and the node compatibility guarantees,
if such are not yet documented.

We did define such document not long ago for Elixir. In terms of deprecations, we have two terms: "soft-deprecation" and "hard-deprecation". The soft-deprecation is added as soon as a new implementation exists. At this point we don't emit
any warnings, but we do update the docs to say the feature will warn in the future and start to point folks towards better ways.

A hard-deprecation is when we finally start emitting warnings. A hard-deprecation can only be added after an alternative exists for at least 2 Elixir releases. This is very important because it means that, once a feature is hard deprecated,
you know you can use the proposed alternative and that alternative is supported at least two versions back.

This is only necessary if a feature is being replaced. In case a feature is being removed, such as non-smp VM versions, you may skip directly to the "hard-deprecation" and emit warnings straight-away since there won’t be an alternative
in the future anyway.

I am not proposing for Erlang/OTP team to follow those rules and conventions but writing *some* rules as minimum guarantees may improve communication and help the community plan in terms of warnings, deprecations and removals accordingly.
I would just avoid emitting deprecation warnings in the same version that an alternative is introduced, because it means library developers need to either only support the latest version or introduce conditionals (either at compile-time or runtime) to support
multiple versions.

Re: Erlang 21, Stability and the murder of an innocent Statemachine

What about documentation from the OTP team that outlines a deprecation policy? It may be a good opportunity to also outline other compatibility guarantees, such as the compiled bytecode guarantees and the node compatibility guarantees, if such are not yet documented.

I think it is a good idea to describe the OTP policy regarding deprecation, backward compatibility, supported releases etc. in one place. Will try to have it available before the OTP 21 release.

The Elixir policy with hard and soft deperecation is also interesting as we need to make it

clearer what a depercation means.

But in short we use the deprecation mechanism to flag that a function och application is no longer recommended for use in new code since there exist another solution that we recomment to be used instead.

We don't remove deprecated functions or applications just like that and some functions have to stay for a very long time (or forever) since there is so much usage of them.

gen_fsm is an old module which is used a lot and it is not likely to dissapear in a near future. I realize that the deprecated attribute inside the module like this-deprecated({start, 3, next_major_release}). is somewhat misleading and we will try to improve this.

/Kenneth, Erlang/OTP

We did define such document not long ago for Elixir. In terms of deprecations, we have two terms: "soft-deprecation" and "hard-deprecation". The soft-deprecation is added as soon as a new implementation exists. At this point we don't emit any warnings, but we do update the docs to say the feature will warn in the future and start to point folks towards better ways.

A hard-deprecation is when we finally start emitting warnings. A hard-deprecation can only be added after an alternative exists for at least 2 Elixir releases. This is very important because it means that, once a feature is hard deprecated, you know you can use the proposed alternative and that alternative is supported at least two versions back.

This is only necessary if a feature is being replaced. In case a feature is being removed, such as non-smp VM versions, you may skip directly to the "hard-deprecation" and emit warnings straight-away since there won’t be an alternative in the future anyway.

I am not proposing for Erlang/OTP team to follow those rules and conventions but writing *some* rules as minimum guarantees may improve communication and help the community plan in terms of warnings, deprecations and removals accordingly. I would just avoid emitting deprecation warnings in the same version that an alternative is introduced, because it means library developers need to either only support the latest version or introduce conditionals (either at compile-time or runtime) to support multiple versions.